This invention relates generally to computed tomography (CT) imaging, and more particularly, to methods and apparatus for artifact reduction in a CT systems that are particularly useful for such systems having a wide bore geometry.
Although the Feldkamp algorithm has been shown to be effective in combating cone beam artifacts for moderate cone angles, it has a disadvantage of reduced z-axis coverage relative to some other image reconstruction methods. For example to ensure artifact-free reconstruction, every voxel in an image must be sampled by all projections. In practice, to obtain a continuous reconstruction volume with multiple axial scans, the reconstructed volume for each scan is limited, as is the distance between adjacent axial scans. For example, in at least one known CT system, the cylindrical volume that can be covered by each axial scan is limited to 10.8 mm. To obtain a continuous coverage of an organ, the distance between adjacent scans is limited to 10.8 mm, which is half the detector z-coverage at the isocenter. To reconstruct a volume of 20 mm, extrapolation has to be performed to utilize the FDK (Feldkamp) reconstruction algorithm. However, this extrapolation introduces artifacts into the reconstructed image.